Creating Threads - Python Concurrency for Senior Engineering Interviews

# Creating Threads

We can create threads in Python using the Thread class. The constructor for the thread class appears below:

Thread constructor#

Thread(group=None, target=None, name=None, args=(), kwargs={}, *, daemon=None)

The group argument is reserved for future extensions. target is the code that the thread being created will execute. It can be any callable object. A callable object can be a function or an object of a class that has the __call__ method. Next, we can pass the arguments to the target either as a tuple args or as a dictionary of key value pairs using kwargs. Finally, the constructor takes a boolean specifying if the thread being created should be treated as a daemon thread.

The below snippet creates a thread using the Thread class's constructor:

Creating thread#

from threading import Thread from threading import current_thread def thread_task(a, b, c, key1, key2): print("{0} received the arguments: {1} {2} {3} {4} {5}".format(current_thread().getName(), a, b, c, key1, key2)) myThread = Thread(group=None, # reserved target=thread_task, # callable object name="demoThread", # name of thread args=(1, 2, 3), # arguments passed to the target kwargs={'key1': 777, 'key2': 111}, # dictionary of keyword arguments daemon=None # set true to make the thread a daemon ) myThread.start() # start the thread myThread.join() # wait for the thread to complete

The above code appears as a runnable snippet below:

from threading import Thread
from threading import current_thread
def thread_task(a, b, c, key1, key2):
    print("{0} received the arguments: {1} {2} {3} {4} {5}".format(current_thread().getName(), a, b, c, key1, key2))
myThread = Thread(group=None,  # reserved
                  target=thread_task,  # callable object
                  name="demoThread",  # name of thread
                  args=(1, 2, 3),  # arguments passed to the target
                  kwargs={'key1': 777,
                          'key2': 111},  # dictionary of keyword arguments
                  daemon=None  # set true to make the thread a daemon
                  )
myThread.start()  # start the thread
myThread.join()  # wait for the thread to complete

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Creating and Running a Thread

Once the thread object is created, we must start it by invoking the start() method. Once started, the thread will execute the target.

Main Thread#

The astute reader would realize that there has to be another thread that is actually executing the code we wrote to create a new thread. This ab initio thread is called the main thread. Under normal conditions, the main thread is the thread from which the Python interpreter was started. The below image captures the above script in debug mode. Notice the debugger dropdown displays two threads:

Main Thread
demoThread